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235 lines
10 KiB
Scheme
235 lines
10 KiB
Scheme
(module lex mzscheme
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;; Provides the syntax used to create lexers and the functions needed to
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;; create and use the buffer that the lexer reads from. See doc.txt.
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(require-for-syntax "private-lex/util.ss"
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"private-lex/actions.ss"
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"private-lex/front.ss")
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(require (lib "readerr.ss" "syntax")
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(lib "cffi.ss" "compiler")
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"private-lex/token.ss")
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(provide lexer lexer-src-pos define-lex-abbrev define-lex-abbrevs
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get-position position-offset position-line position-col position?
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define-tokens define-empty-tokens token-name token-value token? file-path)
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(define file-path (make-parameter #f))
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(define-syntaxes (lexer lexer-src-pos)
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(let ((build-lexer
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(lambda (wrap?)
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(lambda (stx)
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(syntax-case stx ()
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((_)
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(raise-syntax-error #f "empty lexer is not allowed" stx))
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((_ re-act ...)
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(begin
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(for-each
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(lambda (x)
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(syntax-case x ()
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((re act) (void))
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(_ (raise-syntax-error 'lexer
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"expects regular expression / action pairs"
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x))))
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(syntax->list (syntax (re-act ...))))
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(let* ((spec/re-act-lst
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(syntax->list (syntax (re-act ...))))
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(eof-act
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(get-special-action spec/re-act-lst 'eof #''eof))
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(spec-act
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(get-special-action spec/re-act-lst 'special #'(void)))
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(spec-error-act
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(get-special-action spec/re-act-lst 'special-error #'(raise exception)))
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(spec-comment-act
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(get-special-action spec/re-act-lst 'special-comment #'#f))
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(re-act-lst
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(filter-out-specials spec/re-act-lst
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'(special special-comment special-error eof))))
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(let-values (((trans start actions no-look)
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(build-lexer re-act-lst)))
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(with-syntax ((start-state-stx start)
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(trans-table-stx trans)
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(no-lookahead-stx no-look)
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(actions-stx `(vector ,@(map (lambda (a)
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(if a (wrap-action a 'lexeme #'here a) #f))
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(vector->list actions))))
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(spec-act-stx
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(wrap-action spec-act 'special #'here spec-act))
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(spec-error-act-stx
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(wrap-action spec-error-act 'exception #'here spec-error-act))
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(has-comment-act?-stx (if (syntax-e spec-comment-act) #t #f))
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(spec-comment-act-stx
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(wrap-action spec-comment-act (gensym) #'here spec-comment-act))
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(eof-act-stx
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(wrap-action eof-act 'lexeme #'here eof-act))
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(wrap? wrap?))
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(syntax
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(lexer-body start-state-stx
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trans-table-stx
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actions-stx
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no-lookahead-stx
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spec-act-stx
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spec-error-act-stx
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has-comment-act?-stx
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spec-comment-act-stx
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eof-act-stx
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wrap?))))))))))))
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(values
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(build-lexer #f)
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(build-lexer #t))))
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(define-syntax (define-lex-abbrev stx)
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(syntax-case stx ()
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((_ name re)
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(syntax
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(define-syntax name
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(make-lex-abbrev (quote-syntax re)))))
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(_
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(raise-syntax-error
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#f
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"Form should be (define-lex-abbrev name re)"
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stx))))
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(define-syntax (define-lex-abbrevs stx)
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(syntax-case stx ()
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((_ x ...)
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(let* ((abbrev (syntax->list (syntax (x ...))))
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(r (map (lambda (a)
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(syntax-case a ()
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((name re)
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(identifier? (syntax name))
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(syntax (define-lex-abbrev name re)))
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(_ (raise-syntax-error
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'Lexer-abbreviation
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"Form should be (identifier value)"
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a))))
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abbrev)))
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(datum->syntax-object
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#'here
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(cons 'begin r)
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stx)))
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(_
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(raise-syntax-error
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#f
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"Form should be (define-lex-abbrevs (name re) ...)"
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stx))))
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(define (lexer-body start-state trans-table actions no-lookahead
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special-action special-error-action
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has-special-comment-action? special-comment-action eof-action wrap?)
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(letrec ((lexer
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(lambda (ip)
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(unless (input-port? ip)
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(raise-type-error
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'lexer
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"input-port"
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0
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ip))
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(let ((first-pos (get-position ip))
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(first-char (peek-char-or-special ip 0)))
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(cond
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((eq? 'special first-char)
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(let* ((comment? #f)
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(error? #f)
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(spec (with-handlers ((exn:special-comment?
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(lambda (x) (set! comment? #t)))
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(not-break-exn?
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(lambda (ex) (set! error? #t) ex)))
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(read-char-or-special ip))))
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(cond
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((and comment? (not has-special-comment-action?))
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(lexer ip))
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(else
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(do-match ip first-pos (cond
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(comment? special-comment-action)
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(error? special-error-action)
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(else special-action))
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spec wrap?)))))
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((eof-object? first-char)
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(do-match ip first-pos eof-action (read-char-or-special ip) wrap?))
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(else
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(let lexer-loop (
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;; current-state
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(state start-state)
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;; the character to transition on
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(char first-char)
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;; action for the longest match seen thus far
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;; including a match at the current state
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(longest-match-action
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(vector-ref actions start-state))
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;; how many characters have been read
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;; including the one just read
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(length 1)
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;; how many characters are in the longest match
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(longest-match-length 0))
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(let ((next-state
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(cond
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((eof-object? char) #f)
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((eq? char 'special) #f)
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(else
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(vector-ref
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trans-table
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(+ (char->integer char) (* 256 state)))))))
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(cond
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((not next-state)
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(check-match ip first-pos longest-match-length
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length longest-match-action wrap?))
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((vector-ref no-lookahead next-state)
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(let ((act (vector-ref actions next-state)))
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(check-match ip
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first-pos
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(if act length longest-match-length)
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length
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(if act act longest-match-action)
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wrap?)))
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(else
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(let ((act (vector-ref actions next-state)))
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(lexer-loop next-state
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(peek-char-or-special ip length)
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(if act
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act
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longest-match-action)
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(add1 length)
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(if act
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length
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longest-match-length)))))))))))))
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lexer))
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(define id (lambda (x) x))
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(define (check-match lb first-pos longest-match-length length longest-match-action wrap?)
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(unless longest-match-action
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(let* ((match (read-string length lb))
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(end-pos (get-position lb)))
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(raise-read-error
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(format "lexer: No match found in input starting with: ~a" match)
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(file-path)
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(position-line first-pos)
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(position-col first-pos)
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(position-offset first-pos)
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(- (position-offset end-pos) (position-offset first-pos)))))
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(let ((match (read-string longest-match-length lb)))
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(do-match lb first-pos longest-match-action match wrap?)))
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(define (do-match ip first-pos action value wrap?)
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(let ((end-pos (get-position ip)))
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(cond
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(wrap?
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(let/ec ret
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(list (action first-pos end-pos value ret ip)
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first-pos
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end-pos)))
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(else
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(action first-pos end-pos value id ip)))))
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(define-struct position (offset line col))
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(define (get-position ip)
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(let-values (((line col off) (port-next-location ip)))
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(make-position off line col)))
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)
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